The present invention relates to packaging, and more particularly to a device for dispensing a top sheet to cover the top of a load in a stretch wrapping process.
Machines which wrap the sides of a load with a web of stretched material to cover and contain the load are generally known as stretch wrapping machines. Examples of such machines are disclosed in U.S. Pat. Nos. 4,232,501, 4,300,326 and 4,735,033 to Stackhouse and assigned to Lantech, Inc. These patents and the U.S. patents cited in these references are incorporated herein by reference.
If it is desirable to cover the top of the load in a mechanized way, additional components are added to the stretch wrapping machines. Such components dispense and position a sheet of material over the top of the load and hold it in place while it is secured in position.
A number of techniques have been used to cove the top of a load. In one technique, a roll of film is supported on a frame above the load. The leading end of the film is pulled in a horizontal direction with a gripper to unwind a web of film from the roll and position the web across the top of the load. A platen above the severed web is lowered, holding the web against the top of the load and the trailing end of the web is severed, leaving a top sheet on the load to be secured by further stretch wrapping its periphery to the sides of the load or by another manner.
This technique involves a substantial number of additional mechanical components which are expensive to manufacture, such as the gripper and the platen. The effective operation of the gripper is complex and requires high precision to obtain reliability. The cycling time for dispensing the film from the roll, the gripper movement across the top of the load and the movement of the platen substantially slows the wrapping process.
Another conventional technique is to dispense the web of film from the film roll so that it hangs vertically from the film roll and is drawn over the top of the load by a bar which circulates horizontally over the top of the load. This technique reduces the complexity required by the gripper technique. However, having dispensed and exposed the film from the roll before drawing it over the top of the load, and reversing its orientation from a vertical plane to a horizontal plane, increases the likelihood that the film will be twisted, bunched or snagged by the time it is positioned on top of the load, rendering it unusable.
Accordingly, it is an object of the present invention to overcome these drawbacks and provide a device which covers the top of the load with a top sheet, in a simple, quick, inexpensive and reliable manner.
Additional advantages of the invention are set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.